Process of refining lead



atented Aug. llll, llQZfi marten stares earenrorica.

HENRY M. SQHLEICHER, OF ROOSEVELT, AND HARVEY M. BURKEY, 0F PLAINFIELD, NEW JERSEY, ASSIGNORS TO AMERICAN METAL COMPANY, LTD, OF NEW YURK,

N. Y., A CORPORATION OF NEW YORK.

'Paocu'ss or REFINING LEAD.

1\To Drawing.

T 0 all whom it may concern:

. Be it known that we, l-lnrmr M. Sorrnnrorrnn and HARVEY M. BURKEY. citi- Zens of the United States, residing at mosevelt, Middlesex County, New Jersey, and Plainfield, Union County, New Jersey. respectively, have invented certain new and useful Improvements in Processes of Refining Lead; and we do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to a process of refining lead, and particularly to the removal of arsenic, antimony and tin from lead and lead alloys such as lead bullion and antimonial or hard lead: The process may also be advantageously employed'in the removal of.,sulphur, selenium, tellurium and similar elements which are frequently present in crude lead.

The processes of refining lead as heretofore used are subject to certain disadvantages, particularly in the time required for the treatment and in the difficulty experienced in accomplishing the desired separa tion, and it is the object of the present invention to provide a simple and economical process whereby impurities present in crude lead maybe separated readily therefrom.

A further object of the invention is the provision of a process whereby arsenic and antimony may be separately recovered from crude lead. the process thus enabling production of these elements or their compounds as by-products of the refining operation.

Another and particular object of the present invention is the improvement of a process described in our oo-pending application Serial No. 512,630, filed November 3,1921, whereby the time required to complete the refining operation may be materially reduced. Further objects and advantages of the invention will be apparent as itis better understood by reference to the following specification in which the preferred embodiments of the invention are described.

lln the application above referred to, we

Application filed March 13, 1922. Serial-No. 543,471.

have described in detail a process of refining lead involving the oxidation of the impurities present in the lead in the presence of a molten material having an aflinity for these impurities. The process involves covering a molten bath of lead with a molten layer of an alkali metal compound and introducing air under pressure to the bath to provide the oxidlzing condition whereby the impurities are oxidized and carried into the overlying layer. This layer may be skimmed from the surface of the bath and treated for the recovery of the metalloids.

The process described depends for its success primarily upon the fact that lead, while very hot. may be blown with air without forming any appreciable amount of litharge if the metal is covered with a molten alkali metal compound and if there is present in the bath of lead any element having a greater aflinity for oxygen and especially any of the class of elements known as metalloids. Both of these conditions are I essential because pure lead (99.95% lead) will oxidize under the alkali metal compound, and, on the other hand, thepresence of arsenic, antimony or other metalloids will not prevent the formation of litharge when no alkali metal compound is present. In the course of our further study of the process of the prior application, we' have discovered that the preferential oxidation of the contaminating elements results from the presence of small amounts of alkali metal in the bath of impure lead. Thus, when the metalloids are oxidized by the passage of air through the metal, the oxide compounds of the metalloids rise to the surface and react with the molten alkali metal compounds. amounts of alkali metal constitutes the reason for the selective oxidizing action of the air, but owing to the relatively small amounts of alkali metal thus produced, the action is comparatively slow, and, as set forth in the earlier application, the successive treatments each consume approximately one hour.

We have discovered that by the addition of alkali metal in a metallic condition to the lead bath, the reaction rate may be increased The presence of these small materially to a point in fact which permits the successive treatments to consume only from fifteen to twenty minutes. Thusthe capacity of the equipment used may be multiplied from three to four times with corresponding saving in the cost of the refining operation.

As stated, an alkali metal such as metallic sodium may be added directly to the lead bath while the latter is covered by a layer of an alkali metal compound, and. upon the introduction of the blast of air, selective oxidation will occur rapidly with the result that the antimony and other metalloids present will be oxidized and carried into the overlyinp; alkali metal compound layer. The alkali metal in the bath apparently acts as a catalyzer since it remains therein until substantially all of the metalloids have been eliminated. Thealkali metal is then also eliminated, probably combining with the small amount of litharge which is formed at the end of the treatment, and which serves by its appearance as an indication that the reaction is-completed. The lead bath, after the completion of the treatment is free from alkali metal.

It is preferable, however, to employ the alkali metal in the form of an alloy. Thus a sodium lead alloy may be utilized. A sodium. antimony alloy is also suitable for use, and in the further treatment the antimony may be recovered for further use. One advantageous method of thus recovering the antimony -is to leach the/slag for the purpose of recovering the excess of alkali metal compound. The antimony com'- pound is insoluble and is readily separated. By heating this compound with a proportion, e. g., 15% of charcoal, a metallic mass is obtained which consists essentially of antimony with 15 to 20% of metallic sodium. The metallic mass may be introduced into the bath of molten lead with very satisfactory results.

As a specific example of the application of the invention, we have found that by adding an alloy of lead or antimony containing 15 to 20% of metallic sodium to the bath of molten lead in an amount equal to approximately five tenths of 1% of the weight of the metal bath and then subjecting the bath to the blast of air, the desired sepa ration of metalloids may be accomplished in from fifteen to twenty minutes, that is to say, the proportion of the metalloids which may be removed in a single treatment may be oxidized and carriedinto the overlying layer of alkali metal compound in the time mentioned. In practical operations, it is sufficient that a proportion of caustic soda or other suitable alkali amounting to 2.5% of the weight of the metal bath be disposed as a layer thereon and that an alkali metal in a free'oondition or combined as an alloy with lead or antimony, for example, be added to the bath in such proportion that the alkali metal shall amount to approximately one-tenth of 1% of the weight of the bath.

It is not necessary to add alkali metal each time a layer of caustic alkali is added. One such addition may sutiice for the entire operation. The air is not introduced into the bath during skimming or while adding a new lot of caustic alkali.

It is to be understood that after each period of blowing when the layer of alkali metal compound has begun to stiffen, it is removed and the operation is repeated until substantially all of the metalloids have been separated.

The-process is preferably carried out in a suitable iron or steel pot or converter which is heated by a furnace to a temperature of from 625 to 700 C. The converter is provided with tuyeres throughwhich the air, which is preferably pro-heated, is introduced to the lead bath. The tuveresinay extend into the bath for some distance to insure the proper dissemination of the air therein.

The skimmings from the "lead bath. consisting of the alkali metal compound with oxidized metalloids combine-d therewith. are thrown into water with the resulting production of a strong caustic solution and an insoluble residue. The solution is decanted and the residue is dried and treated for the recovery of antimony or antimony compounds, or as hereinbefore set forth, a proportion of the antimony compounds may be reduced to provide the antimony sodium alloy for the further treatment of the lead bath. The residue contains substantially 60% of antimony mostly in pentavalent state, about 18% of sodium oxide. and small amounts of iron and lead. Any lead shot carried overin the caustic soda may be sepa rated from the antimony residue and returned to the lead bath. The solution is subjected to a suitable precipitating agent to throw out the arsenic which may be worked up to produce arsenic or arsenic compounds. The solution 18 then evaporated preferably by flue gases from the melting furnace, and when concentrated and fused,

the caustic soda may be reused.

If the lead bullioncontains arsenic and antimony, the greater part of the arsenic is eliminated in the early part of the process, that is to say. in the first skimming's of caustic soda. Substantially all of the arsenic is soluble so that it is almost completely separated from the antimony.

If tin be present it is also soluble and may be recovered by suitable treatment.

Any silver which may be present in the lead remains therewith since it is unaffected by the processand does not enter the skimmings. The sllver may be separated from.

- Various changes may be made in the dethe lead after the completion of the process in accordance with the usual practice.

From the foregoing, it will be understoocl that the process herein described provides for the effective separation of impurities from lead in a simpleand economical man ner, and particularly in a more rapid manher than is possible under the practice described in the earlier application. Soft leadmay be produced from lead containing con siderable quantities of arsenic and antimony With a minimum of expense.

molten material capable of combining with oxides of the impurities present in the lead, accelerating the reaction by the addition of an alkali metal to the molten lead, and separating the molten material with the impurities from the lead.

2. A method of refining lead, which comprises subjectingithe molten lead to anoxidizing condition in the presence of a molten material capable of combining with oxides of the impurities presentin the lead,

accelerating the reaction by the addition of molten lead, an separating the molten material with the i purities from the lead.

.3. A method of refining lead,'which com an alloy contaiqnng an alkali metal to the prises subjecting the molten lead to an oxidizing condition in the presence of a molten material capable of combining with oxides of the impurities present in the lead, accelerating the reaction by the addition of an alloy of lead with an alkali metal to the'molten lead, and separating the molten material with the impurities from the lead.

4. A method of refining lead, which comprises-subjecting the molten lead to a currentof an oxidizing gas in the presence of a molten material capable of combining with oxides ofthe impurities present in the lead, accelerating the reaction by the addition of an alkali metal to the molten lead, and separating the'molten material with the impurities from the lead. p

A method of refining lead, which comprises subjecting the molten lead to an oxidizing condition in the presence of a molten alkali metal compound and of an alkali metal, and separating the alkali metal compound with the impurities from the lead.

6. A method of refining lead, which comprises subjecting the molten lead to a current of an oxidizinggas in the presence of a molten alkali metal compound and of'an alkali metal, and separating the alkali metal compound with the impurities from the lead. I

71 A method of refining,lead, which comprises forcing a current of air through the molten lead in the presence of a molten material capable of combining with oxides of pound with the'impurities from the lead.

9. A method of refining lead to remove antimony therefrom,-which comprises forcing a current of air through the molten lead in the presence of an alkali metalhydroxide andof analkali metal, andseparating the alkali metal compound containingantimony from the'lead.

10. A method of refining lead to' remove antimony therefrom, which comprises subjecting the molten'lead to an oxidizing condition in the presence of a molten alkali metal compound and of an alloy containing antimony and an alkali metal, and separating the alkali metal compound containing antimony-from the lead.

11. A method of refining leadt'o remove antimony therefrom, which comprises subjecting the molten lead to an oxidizing condition in the presence of a molten alkali metal compound and of an alloy containing antimony and an alkali metal, separating the alkali metal compound containing antimony from the lead, leaching the alkali metal compound to recover insoluble antimony compounds therefrom, and reducing the antimony compounds, to provide the alloy of antimony with an alkali metal.

12. A method of refining leadto remove mpurities therefrom, which comprises covof a material capable of combining with ox-j ides of the impurities present in the' lead, adding an alkali metal to the molten lead, forcing an oxidizing gas through the mass, and separating the molten material with the impurities from the lead. v

13. A'method of refining lead toremove impurities therefrom, which comprises. covering the molten lead with a molten layer v ering the molten lead with a molten layer of an alkali metal compound, adding an alkali metal to the molten lead,a forcing an oxidizing gas through the mass, and separating the alkali metal compound from the lead. I

14L. A method of refining lead to remove impurities therefrom, which comprises covering the molten lead with a layer of molten material having'a-selective afiinity for the impurities present in the lead, adding an alloy containing an alkali metal to the molten lead, forcing an oxidizing gas through the mass, and separating the molten material with the impurities from the lead.

15.- A method of refining lead, which comprises covering the molten lead with a layer of molten materiahcapable of combining with oxides of the impurities present in the lead, adding an alloy containing lead and an alkali metal to the molten lead, forcing an xidizing gas through the mass, and separating the molten material with the impurities from the lead.

16. A method of refining lead to remove in'ipurities therefrom, which comprises covering the molten lead with a molten layer of an alkali metal compound, adding an alloy containing an alkali metal to the molten lead, forcing an oxidizing gas through the mass, and separating-the alkali metal com pound from the lead.

17. A method of refining lead to remove impurities therefrom, which comprises covering the molten lead with a molten layer of an alkali metal compound, adding an al ali metal to the molten lead, forcing an OK- idizing gas through the mass, skimming the alkali metal compound from the lead, and repeating the operation with further quantitles of alkali metal compound and alkali metal until the impurities are substantially exhausted.

impurities therefrom, which comprises covering the molten lead With a molten layer 18. A method of refining lead to remove of an alkali metal compound, adding an alkali metal to the molten lead, forcing an oxidizing gas through the mass, skimming the alkali metal compound from the lead, repeating the operation with further quantities of alkali metal compound and alkali metal until the impurities are substantially exhausted, leaching the skimmings to separate insoluble material from the alkali metal compound, evaporating the solution and returning the recovered alkali metal compound for further use. I

19. A method of refininglead to remove impurities therefrom, which comprises sub jccting the impurities in the molten lead to selective oxidation in the presence of an alkali metal.

20. A method of refining lead to remove impurities therefrom, which comprises sub vjecting the impurities in the molten lead to selective oxidation in the presence of' an alkali metal added to the lead in theform of an alloy.

21. A method of refining lead, which comprises subjecting the molten lead to an oxidizing condition in the presence of an alkali metal.

A method of refining lead, which comalkali metal and in the presence of a molten alkali metal compound.

In testimony whereof we affix our signatures.

HENRY M. SCHLEIGHER. HARVEYM; BURKEY. 

